Features: Update the default_dialect test for old GNU-like compilers.

Prior to GNU 4.7, GNU defined __cplusplus incorrectly, and defined
__GXX_EXPERIMENTAL_CXX0X__ in C++11 mode.

Tests/CompileFeatures/default_dialect.cpp

@@ -14,7 +14,7 @@ Outputter<__cplusplus> o;
 #  if !DEFAULT_CXX98
 #    error Buildsystem error
 #  endif
-#  if __cplusplus != 199711L
+#  if __cplusplus != 199711L && __cplusplus != 1 && !defined(__GXX_EXPERIMENTAL_CXX0X__)
 Outputter<__cplusplus> o;
 #  endif
 #endif